The present invention relates to a scanning probe microscope using fluorescent light capable of measuring various data by utilizing a fluorescence phenomenon while recognizing the positional relationship between a probe and a sample.
In the conventional scanning probe microscope using fluorescent light of this type, the probe is coated with a fluorescent material emitting a fluorescent light when excited by a light of a predetermined wavelength. On the other hand, the sample set in a microscope stage is also coated with a fluorescent material emitting a fluorescent light when excited by a light of a predetermined wavelength.
If the sample and the probe are irradiated with light having the predetermined wavelength in starting the data measurement, a fluorescent light is emitted from each of the probe and the sample.
Where the probe is positioned as desired relative to the sample position in performing the actual measurement, the microscope stage is moved while monitoring the positional relationship between the fluorescent light images of the probe and the sample by, for example, a CCD camera. When overlapping has taken place between these two fluorescent light images, the probe is regarded as being positioned as desired relative to the sample. Under this condition, various data of the sample are measured.
When it comes to a scanning probe microscope using fluorescent light in which the sample is scanned with a resolution of about sub-micron to sub-nanometer order, the positional relationship between the probe tip and the sample is required to be recognized with a high precision.
In the conventional scanning probe microscope using fluorescent light, it is certainly possible to position the probe somewhat close to a desired position relative to the sample position. However, it is difficult to recognize the positional relationship between the probe tip and the sample with a high precision. To be more specific, the fluorescent light emitted from each of the probe and the sample is diffused around the probe tip and the sample, with the result that the probe tip and the sample are buried in the fluorescent light images. It follows that, even if each of these fluorescent light images is monitored by a CCD camera, it is very difficult to recognize based on the fluorescent light images the positional relationship between the probe tip and the sample with a high precision.
As pointed out above, the conventional scanning probe microscope using fluorescent light is defective in that it is difficult to determine accurately how much the probe tip is deviated in the lateral direction (that is, XY direction) from the sample. It is also difficult to determine accurately the distance that is, the distance in Z direction between the probe tip and the sample, even where the probe tip is positioned right above the sample.
What should also be noted is that, where a substance other than the sample emits a fluorescent light of a color equal to that of the fluorescent light emitted from the sample, by self-excitation, it is difficult to determine whether the fluorescent light image, which is being observed, is formed by the fluorescent light emitted from the sample or said other substance. In this case, it is possible for the probe to be positioned erroneously relative to said other substance.